Outrunning the Bear

Two hikers are out hiking. All of a sudden, a bear starts chasing them.
They climb a tree, but the bear starts climbing up the tree after them.
The first hiker gets his sneakers out of his knapsack and starts putting them on.

The second hiker says:

- What are you doing?

The first responds:

- I figure when the bear gets close to us, we'll have to jump down and make a run for it.

The second says:

- Are you crazy? Don't you know you can't outrun a bear?

The first guy says:

- I don't have to outrun the bear... I only have to outrun you!